1. Field of the Invention
The present invention relates to a method of manufacturing a III-V Group compound semiconductor device and, more particularly, to a method of manufacturing a III-V Group compound semiconductor device, including the step of forming a magnesium-doped p-type III-V Group compound semiconductor layer by metal organic chemical vapor deposition.
2. Description of the Related Art
Metal organic chemical vapor deposition (MOCVD) is a well-known technique of forming a compound semiconductor layer in the art. In the formation of a p-type III-V Group compound semiconductor by the MOCVD technique, zinc is usually used as a p-type dopant. Zinc exhibits substantially good doping characteristics as a dopant for GaAs. However, when zinc is used as a dopant for a III-V Group compound semiconductor containing phosphorus such as InP or GaInAlP, its doping rate becomes low, and its activation rate is also low. In addition, since a diffusion speed of zinc is too high, it has a poor doping controllability.
As a p-type dopant which can replace zinc, therefore, the use of beryllium or magnesium has been attempted. Beryllium exhibits good characteristics as a p-type dopant in a molecular beam epitaxial growth method. However, since an organic compound of beryllium has a strong toxicity, an application of beryllium to the MOCVD method must be avoided.
An organic compound of magnesium has little problem of toxicity unlike an organic beryllium compound. Examples of such an organic magnesium compound are alkylmagnesium compounds such as dimethylmagnesium and diethylmagnesium. These alkylmagnesium compounds have a very strong self-adsorptive property and have no effective vapor pressure required in the MOCVD method. Although biscyclopentadienylmagnesium (Cp.sub.2 Mg) having a cyclopentadiene with a comparatively high vapor pressure is used, it is very difficult to control doping due to a memory effect (that a doping source adhered on a reaction tube re-enters a reaction system during subsequent processing) remaining in an apparatus. Therefore, a sharp concentration change of 10.sup.3 /cm.sup.3 or more in a 0.1 .mu.m distance, which is normally required for a device, cannot be obtained. In addition, bismethylcyclopentadienylmagnesium ((CH.sub.3).sub.2 Cp.sub.2 Mg) having methyl group introduced on each cyclopentadiene to increase a vapor pressure has been used. However, a sufficiently sharp or steep concentration change is not obtained.
As described above, an alkyl compound of magnesium has only a low vapor pressure, and a magnesium compound having a cyclopentadiene has a strong memory effect to make it difficult to perform doping with good controllability.